The present invention relates to improvements in echo ranging vehicle occupant location sensing.
Within a vehicle occupant protection system, it is known to control (e.g., adjust) an inflation profile of an air bag based upon a distance between a vehicle occupant and the air bag to enhance protection of the occupant. Such control is suitable for a scenario in which the distance between the occupant and the air bag assembly changes during a pre-crash braking condition. Specifically, during a pre-crash braking condition, the vehicle decelerates and the inertia of the occupant causes the occupant to move forward relative to the seat toward an instrument panel that contains the air bag assembly. Also, it is known to control other air bag deployment aspects based upon the distance between the occupant and the air bag assembly and/or another occupant location characteristic to enhance protection of the occupant.
A known vehicle occupant protection system includes an echo ranging system to determine the distance between the air bag and the vehicle occupant. An echo ranging system operates by emitting a short burst of a carrier signal that travels directly between an emitter and the vehicle occupant. The emitted signal bounces on the vehicle occupant and the bounced signal returns to a receiver as an echo of the emitted signal. The echo ranging system includes a time-of-flight distance determination system that determines the time elapsed between the emission of the signal from the emitter and the return of the echo at the receiver and from this time differential determines the distance between the occupant and the air bag assembly.
Ideally, the time period between signal emission and echo reception is long enough to allow the signal to travel to the occupant and return before the emission of a subsequent signal. However, if the occupant is located sufficiently far away, then the return echo returns after a subsequent signal is emitted. Such a return echo can be termed a late echo. Also, although it is intended to bounce the signal on the vehicle occupant, it is possible that the signal may bounce on other surfaces within the vehicle. This situation occurs if the occupant turns or leans and the signal bounces on the occupant""s seat, on the back seat, or on other surfaces within the vehicle. Such other surfaces may also be located sufficiently far to cause return of a late echo.
The result is that the time-of-flight distance determination system may calculate the time interval between the subsequent emitted signal and the receipt of the return echo (i.e., late echo) associated with the prior emitted signal and thereby miscalculate the distance to be closer than actuality. Therefore, the occupant protection system would not provide optimum enhancement of occupant protection.
One particular type of echo ranging system includes a head unit that incorporates three ultrasonic transmitters and three ultrasonic receivers for emitting and receiving ultrasonic signals. The invention provides for a method of differentiating between ultrasonic signals generated from transmitters physically separated from each other so that a receiver can identify the source of each ultrasonic signal that is received.
Another type of echo ranging system is a system that locates the occupant by emitting and receiving ultrasonic signals using two or more ultrasonic transducers. These transducers are located in various locations in the vehicle passenger compartment. As a result, by implementing multiple transducers and by placing each transducer in a different location, each transducer receives the return signal associated with the signal that each individual transducer emitted.
In accordance with one aspect, the present invention provides an apparatus for determining a vehicle occupant location characteristic. The apparatus includes means for echo ranging at a first ultrasonic frequency to determine a first time-of-flight to an occupant seating position. The apparatus includes means for echo ranging at a second ultrasonic frequency to determine a second time-of-flight to the occupant seating position. The apparatus also includes means for determining the occupant location characteristic using at least one of the determined times-of-flight.
In accordance with another aspect, the present invention provides a method of determining a vehicle occupant location characteristic. The method includes echo ranging at a first ultrasonic frequency to determine a first time-of-flight to an occupant seating position. The method includes echo ranging at a second ultrasonic frequency to determine a second time-of-flight to the occupant seating position. The method also includes determining the occupant location characteristic using at least one of the determined times-of-flight.